"I'm not sure what governs sorting in the on-line trees..."
We're just not on that need-to-know list.
"Use a Fact Name before "D(eath)" - for example: Address, with the same date as the death date. Does it come before Death in the on-line tree?"
Both "Address" and "Residence" facts get sequenced below the "Death" event. Nor are they alphabetized.(see attached)
"Maybe an enhancement request is in order?"
Precisely...and I'd imagine that making "Death" the default last "fact" in identical calendar days should be programming child's play.